Formation of Methylglyoxal in Reduced Nicotinamide Adenine Dinucleotide Phosphate-Dependent Lipid Peroxidation of Rat Liver Microsomes

The formation of methylglyoxal in rat liver microsomes by reduced nicotinamide adenine dinucleotide phosphate-dependent lipid peroxidation and its binding to proteins were studied. Methylglyoxal in the microsomes of rat liver after enzymic lipid peroxidation was identified as its fluorescent derivative, 2-(2-benzimidazolyl)-3-methyl-quinoxaline, by gas chromatographymass spectrometric determination. The contents of both thiobarbituric acid reactive substances and methylglyoxal showed time-dependent increases until 80 min after the start of lipid peroxidation. The production of thiobarbituric acid reactive substances and methylglyoxal in microsomes by lipid peroxidation was supressed by heat treatment (24.3 and 26.3%, respectively) and by the addition of catalase (EC 1.11.1.6) (28.5 and 67.1%) or superoxide dismutase (EC 1.15.1.1) (74.3 and 49.9%). Methylglyoxal, formed in microsomes by the peroxidation, existed in the high molecular weight fractions of the reaction mixture, which were separated by gel filtration chromatography with a Sephadex G-25 column. These results suggest that methylglyoxal derived by enzymic lipid peroxidation in rat liver microsomes binds readily to microsomal proteins.